Preparation of alkali cellulose



Patented Feb. 24, 1942 UNITED STATES PATENT OFFICE PREPARATION OF ALKALICELLULOSE Johann Joseph Stoeckly and Richard Bartunek, Teltow-Seeh'of,Germany, assignors to North American Rayon Corporation, New York, N. Y.,a corporation of Delaware No Drawing. Application April 9, 1940, Serial4 Claims.

'I'his invention relates to improvements in lmethods for preparingalkali cellulose.

It is one of the objects of the invention to produce an alkali celluloseadapted for the manufacture of viscose and from which deleteriousvarieties of cellulose, for example the hemicellulose and principallybeta cellulose are substantially eliminated at the outset so as toinsure their absence during the viscose producing operations. To thisend the invention contemplates the provision of treatment procedures andsteps adapted to achieve the aforesaid purpose and also to permit theproduction of an alkali cellulose which iurthermore can be properly andthoroughly xanthated.

It is a further object of the invention to provide a method for theaforesaid purposes which is capable of application without requiringextensive alteration of existing equipment as used in the present stateof the viscose manufacturing art.. I I The usual method for producingviscose. has

. the drawback that the hemicellulose and especially the so-called betacellulose is eliminated in a far too inadequate manner and'amount. Whenan ordinary dip lye is used having a caustic soda content of about 18per cent it is mainly only In Germany March- 31, 1939 the very easilysoluble gamma cellulose which is dissolvedout of the cellulosic rawmaterial durart to soak cellulosic raw material in a caustic soda lye ofa concentration lower than that'capable of producing mercerization, todrain it with the aid of pressure, and then to mercerize it in aknownmanner by a second dipping procedure. This prior art methodhowever alsohas the drawbacks of, first, requiring a too prolonged dipping time anda very extensive apparatus layout for the dipping and circulation of thelye, and, seccellulose sheets readily fall apart prior to and during thesecond dipping.

In accordance with the present invention however it has been found thatit is possible to start with ordinary cellulosic raw material containinghemicellulose, say, either sulphite cellulose, spruce cellulose, or evenalkali-cooked beechwood cellulose, and to separate out the betacellulose during ,the production per se of the alkali cellulose Withoutrequiring any appreciable alteration of the apparatus customarily usedfor producing the latter.

In accordance'with the method of the invention, the cellulose raw orstarting material is first treated with a caustic soda lye of definitetemperature and of such concentration-as is adapted to exert thegreatest possible dissolving action on the beta cellulose. Under suchconditions, if the reaction time is adequate, substantially all of thebeta cellulose is caused to pass into solution in this dilute dip lyeand can be separated out by subsequent draining and pressing. Whenoperations are conducted at ordinary room temperatures of to C., it ispreferable not to use the same concentration of caustic soda for allvarieties of cellulosic raw material because it has been found that thevarious celluloses require varying concentrations of caustic soda liquorfor achieving the most eificient removal of beta cel-- lulose in theindividual cases. For example, in the case of ordinary sulphitecellulose derived from spruce wood, a concentration of 10 to 11 7 percent is usually required, whereas in the case ondly, in the seconddipping procedure, the strong into the drained but still lye-ladencellulose mass; moreover, when dipping presses are used, the

dip lye diffuses incompletely andnon-uniformly of an alkali-boiledbeechwood cellulose, a 6 to 9 per cent concentration is preferableusingthe same temperature of 15 to 20 C. Th proper concentration can readilybe ascertained by means of preliminary tests.

Cellulosic raw material, dipped, drained and pressed, and freed frombeta cellulose in the manner'aforesaid howeverdoes not yet possess theproperties of a serviceable alkali cellulose that can be xanthated inthe usual manner and usedfor the preparation of viscose since therequired alkali concentration necessary for a mercerized condition isnot present. In accordance with the present invention however it ispossible to produce a serviceable mercerized condition of the cellulosemass during the course per se of the subsequent comminuting anddefibring procedure byinjecting a fine spray ofia more highlyconcentrated caustic soda liquor (as by means of spray nozzles) into theshredder or the cellulose mass', during the shredding operation, say atthe nitiation thereof and-prior to the termination thereof. In this casesuch an amount of caustic soda liquor and of such concentration shouldbe used as is adapted to produce an alkali cellulose of adequate alkaliconcentration which can be readily and properly xanthated. In effectingsuch an increase in the alkali content of the alkali cellulose in themanner described, the usual shredding time of about three hours is amplysufficient. Xanthation of alkali cellulose so produced is accomplishedwithout difiiculty.

In order to avoid the dangers and nuisance caused by the spray ofcaustic lye, it has been found preferable to effect the spray injectionof the caustic soda lye with the aid of spray nozzles in which theliquor is directly subjected to high pressure, that is, with suchnozzles as are adapted to operate without the use of air or otherpropelling gases. The spray injection of the caustic soda lye into thepreliminarily alkalinized cellulose raw material'need not necessarily bedirectly efiected in the shredder but may also be carried out in aseparate device, e. g. a container, with the material of course kept inmotion by suitable means, and after said material has been preliminarilysubjected to a certain amount of caustic soda liquor into the alkalicellulose and the uniform permeation of the entire mass may befacilitated by raising the temperature of the spray injected strongliquor to 30, 40 and even to 50 C., or by allowing the shredder itselfto operate at elevated temperatures, or by using both expedients.Wetting agents may also be added to the spray injected liquor to achievethe same purpose. The use of wetting agents serves facilitate the sprayinjection action, as does also increasing the temperature of the sprayiniected strong liquor. Efiecting the defibring at elevated temperaturesalso has the advantage of permitting the otherwise customarypre-ripening of the alkali cellulose to be largely dispensed with, or,under certain circumstances, to be entirely dispensed with. Severalembodimental examples are given herewith to illustrate the method ofpractising the invention.

Example 1 100 kg. of ordinary air-dry sulphite cellulose having an alphacellulose content of about 8'7 per cent are immersed in sheet form in asoaking press containing 10.5 per cent caustic soda, at a temperature ofC., and after an immersion or soaking period of 1 /2 hours the materialis drained and pressed so as to weigh 230 kg. The pressed material isthen shredded in a shredder, e. g. of the Weiner-Pfleiderer type, asknown in the art, for three hours, and during this period the strengthof the alkali content in the alkali cellulose mass is increased to themercerization point. To effect this, a caustic soda liquor of per centNaOH content is spray-injected into the shredder while it is inoperation and after the material has been preliminarily comminuted as astart, the liquor being run in at such a rate that in 1 hours 80 kg. ofa percent caustic soda lye pass into the alkali cellulose mass. Theshredding is continued without interruption for a period of 3 hours. Thethus obtained, shredded alkali cellulose is then allowed to ripen to thedesired extent in the usual manner, and thereupon worked up intoviscose.

Example 2 kg. of air-dry sulphite cellulose of ordinary quality andhaving an alpha cellulose content of 87 per cent are mixed in flake formwith a 10.5 per cent caustic soda lye in an iron vessel, the mass beingintimately stirred- After one hour the alkali-containing cellulose massis drained and pressed in a suitable press (e. g. a screw conveyor typepress) to a weight of 240 kg., then passed through an attrition orgrinding mill (e. g. of the Eirich type, as known in the art) and thenplaced in a shredder of the Werner-Pileiderer type mentioned above. Theshredder is allowed to run for 3 hours and during the first 1 hours,herein referred to as the step in which initiation of the shredding isefiected, 70 kg. of a 45 per cent caustic soda liquor are spray-injectedtherein by means of spray nozzles of the kind described above. Thealkali cellulose is thereupon worked up into viscose in the usualmanner.

Example 3 100 kg. of air-dry alkali-cooked beechwood cellulose, in sheetform, are immersed in a dipping press containing a 7 per cent causticsoda liquor and at a temperature of 20 and after 1 hours drained andpressed down to a weight of 220 kg. The pressed material is then placedin a shredder and shredded. After a preliminary shredding of one hour(referred to above as the initiation of the shredding step) 100 kg.'of a48 per cent caustic soda liquor are spray-injected therein while theshredding procedure is being continued, the spray injectionv beingcontinued for the course of /2 hour and the total shredding step beingcontinued so as to occupy a total of three hours. The alkali celluloseis thereupon worked up further in the usual manner.

Modifications of this invention will readily be recognized by thoseskilled in the art, and it is desired to cover all variations andmodifications coming within the scope of the appended claims.

What is claimed is:

1. In the process of preparing alkali cellulose, the steps in sequenceconsisting of dipping a hemicellulose-containing cellulose into a dilutecaustic soda lye containing approximately 6 to 11 per cent by weight ofcaustic soda, removing excess lye from said cellulose by pressing,shredding said cellulose and spray-injecting a second caustic soda lyecontaining approximately 30 to 48 percent by weight of caustic soda tomercerize said cellulose 'while. continuing the shredding thereof toform an alkali cellulose.

2. In the process of preparing alkali cellulose, the steps in sequenceconsisting of dipping a hemicellulose-containing cellulose into a dilutecaustic soda lye containing approximately 6 to 11 percent by weight ofcaustic soda, removing excess lye from said cellulose by pressing,shredding said cellulose and spray-injecting a second caustic soda lyecontaining approximately 30 to 48 per cent by weight of caustic soda tomercerize said cellulose while continuing the shredding thereof to forman alkali cellulose, said second lye containing a wetting agent. a

3. In the process of preparing alkali cellulose, the steps consisting ofdipping a sulphite cellulose containing about 87% of alpha-celluloseinto a lye containing approximately 10.5% by weight of caustic soda,removing excess lye from said cellulose by pressing, preliminarilyshredding said cellulose and then spray-injecting a second lyecontaining approximately 30 to 45% by weight of caustic soda in anamount to mercerize said cellulose while continuing the shreddingthereof.

44 In the process of preparing alkali cellulose,

the steps consisting of dipping approximately 100 kgs. of analkali-cooked beechwood cellulose in' sheet form at a temperature ofapproximately 20 C. intoa lye containing approximately 7% by weight ofcaustic soda, removing excess lye after approximately .1 /2 hours bypressing said cellutic soda while continuing said shredding for anotherperiod of approximately 90 minutes.

RICHARD BARTUNEK. JOHANN JOSEPH STOECKLY.

